The overall hypothesis addressed by this program is that non-fibrillar aggregated assemblies of amyloid beta (Abeta) which we refer to as Abeta-derived active ligands (ADALs) are active in triggering Alzheimer's disease (AD)-specific cellular responses leading to glial activation, neuronal plasticity malfunction, degeneration and ultimately cell death. We further propose that the generation of these active supramolecular structures of Abeta aggregates can be influenced by the presence of other plaque components, particularly those components derived from glia, and that responses of glial cells contribute to an environment that facilitates and enhances the formationof these bioactive ADALs. Inherent to our hypothesis is that glia are not just appsive bystanders, but are a part of the pathogenesis process. We postulate that Abeta toxicity can be mediated through its effects on glia, that glia-derived proteins can influence the structure of Abeta and its effects on neurons, and that these processes are relevant to the actual neuropathology seen in the AD brain. The questions being addressed in this subproject are: What are the responses of glial cells to ADALs? How do glial proteins affect the formation of ADALs and their bioactivity? Are glia relevant to AD neuropathology? Three aims are proposed to address these questions. 1) The responses of glial cells to ADALs will be evaluated. Specific Abeta aggregates will be prepared and characterized by project 1. We will test the activity of these ADALs on cultures of rat primary astrocytes, by examining the levels and activity of six relevant glial proteins: alpha1-antichymotrypsin (ACT), apolipoprotein E (apoE), apoJ, butyrylcholinesterase (BchE), interleukin-1 (IL-1) and S100beta. 2) The effects of glia on ADAL formation and neurotoxicity will be evaluated. In co-aggregation experiments, we will evaluate the kinetics of aggregate formation and the structure of Abeta aggregates formed in the presence of these six glial proteins willb e correlated with plaque type in AD brain. We willdetermine the regional distribution and immunoreactive density of specific flial proteins in AD and control brain tissue, and establish correlations with the distribution of non-neuritic vs neuritic plaques. This systematic examination should provide insight into how Abeta affects glia, and how glia participate in amyloid plaque progression and development of neurotoxicity.